There are at present in use two main types of rotary mowers, namely the so-called disc mower and the so-called drum mower. Disc mowers comprise a plurality of relatively flat dish-shaped discs mounted along a transverse drive-casing and each carrying two or more outwardly projecting cutting blades, the discs being rotated in counter-rotating pairs. Drum mowers normally comprise one or more pairs of contra-rotating vertical drum-like members which carry at their lower ends outwardly extending skirts or flanges which in turn carry cutting blades mounted similarly to those on disc mowers. The purpose of drums is to assist inward and rearward movement of the cut crop so as to form regulated swaths behind the mower. Disc mowers may be driven from above or below, but commonly drum mowers depend from an upper frame and are driven from above. The present invention has particular application in connection with drum mowers, but may also have application in connection with disc mowers or other rotary crop cutting apparatus.
The recent trend in development of rotary mowers has been to increase the overall width of cut of the mower, and this has normally been achieved by mounting more small cutting units together on a fixed transverse mounting beam. This has resulted in a wide cutting implement which effects the cutting operation in a single plane and this gives uneven cutting on undulating ground. A further difficulty arises where a wide mower is produced with a multitude of drum cutters, in that a number of separate swaths are produced behind the machine which leads to problems in handling and treating the cut crop.
Another disadvantage which arises with known drum mowers comes from the conventional drive used in which a transverse shaft running across the tops of the drums drives the drums through bevel gears in gear boxes mounted directly on top of the drums. Most drum mowers are driven by direct gearing with a large gear box structure along the top of the drums and direct drive to the drums through the bevel gears. The gear case forms part of the structure of the machine and is subject to distortion and damage while in use. In such arrangements, the set of bevel gears has no protection or shock absorption provided so that it is subjected to high shock loads transmitted from the ground or obstacles met by the cutters while cutting. With the bevel-gear drive system presently used for drum mowers the centre spindle of the drum is driven, which makes it difficult to make a simple and robust design of drum and spindle as it is essential that the centre spindle of the drum is driven.
If an attempt is made to increase the width of cut of a conventional rotary mower by increasing the diameters of the discs or of the skirts of the drums (so as to avoid providing a relatively large number of rotary units) the problems outlined above are magnified by the weight of the resulting machine and the size of drive gear boxes required. It also follows that damage to such gear boxes is more costly if the size of the units is increased. Furthermore, if conventional designs of drum mower are scaled-up the resulting shocks on the drums from use on uneven ground are increased as the width of the rigid transverse mounting for the drum is increased.
A further disadvantage which arises with the drum mowers of conventional nature with relatively small drums is the difficulty of passing the cut crop between the restricted opening between the drums. If the drums are made smaller in relation to the circumference of the cutting blades, the drums become subject to wrapping of the crop around them. These disadvantages of conventional drum mowers again indicate the benefits which would arise from use of larger drum mowers, but mere increase of size of conventional units gives rise to the disadvantages outlined above.